1. Technical Field
The present invention illustrates an optical sensor circuit, and more particularly, the optical sensor circuit having a capability of ambient light resistance.
2. Description of the Prior Art
With the advancement of technologies, various electronic devices with different input interfaces are adopted to our daily life. Specifically, these electronic devices often use an input panel as a communication interface between users and the function-mapping of electronic devices. Users can operate the electronic devices for processing various functions by inputting commands on the input panel, instead of using conventional keyboard or mouse. Generally, two input modes of the input panel can be categorized to an optical sensor input mode and a touch input mode. However, since the touch input mode requires a touch activity for contacting with the input panel, the lifetime of the input panel may be reduced by material abrasion. Thus, the input panel using the optical sensor input mode has a longer lifetime of work than the input panel using the touch input mode.
In the input panel having the optical sensor input mode, the input panel includes a plurality of light sensor units. Each light sensor unit has a plurality of transistors. Particularly, given a negative bias voltage being fixed in each transistor, when an incident light is increased, a light current generated by the transistor is increased accordingly. By using the transistor to generate the light current, the light sensor unit can identify whether the incident light is inputted to the input panel, such the input panel using the optical sensor input mode is usually applied to detect a specific light source. For example, the input panel is used for detecting a red light source from a laser pen with a red color. Specifically, when the input panel is used to detect the specific light source, some transistors of the light sensor unit are covered with corresponding light filters. As known, a light filter can be regarded as a band-pass filter for extracting/passing desired light photons with respect to a predetermined light spectrum band, exclusive of other light photons with respect to other light spectrum bands. For example, when a transistor is covered with a light filter with the red color, the transistor only generates light current by inputting an incident light with the red color. Thus, in this case, the light sensor unit can make a correct response to detect the incident light with the red color from the laser pen.
However, a white ambient light here is considered. Specifically, the white ambient light includes all light spectrum bands of all colors (i.e., R/G/B overlapped spectrum bands). In the conventional optical sensor, when an intensity of the white ambient light is too strong, the light sensor unit may error because the light sensor unit determines the incident light with red color is being inputted to the input panel, even when the laser pen with red color is turned off. The reason is illustrated as below. Since the white ambient light can be decomposed to three original colors (i.e., red, green, and blue), when the intensity of the white ambient light is strong enough, the intensity of red color component of the white ambient light is also proportionally increased. Thus, the light sensor unit makes a wrong decision because of the enhancement of the red color component. In other words, when the light sensor unit receives the white ambient light, the light current (or say, voltage) of the light sensor unit used for detecting the specific light color may be varied in wrong conditions with the intensity of the white ambient light being increased, thereby leading to a severe shadow effect. As a result, since the SNR (Signal-to-Noise Ratio) of the detection mechanism of the light sensor unit is reduced, a probability of false alarm/error detection of the light sensor unit is increased.
Thus, to develop an optical sensor circuit having a capability of ambient light resistance is important.